The present invention relates to an idler pulley, particularly to an idler pulley adapted to have entrained therearound a timing belt for automobile engines or an auxiliary machine driving belt, such belt being destined to be heavily loaded.
Idler pulleys are installed to increase the wrapping angle of a belt, such as a timing belt for automobile engines or an auxiliary machine driving belt, so as to impart a suitable tension to the belt.
Some idler pulleys are of the type in which a pulley main body formed of a steel plate and having a pulley peripheral surface around which a belt is entrained is force-fitted on the outer ring of a rolling bearing, the pulley main body having a phosphate treatment applied thereto to prevent corrosion, etc.
As shown in FIG. 3, when this type of idler pulley is subjected to a load (radial load) from a belt entrained therearound, the pulley main body 1 and bearing 2 are slightly deformed. However, since the deformation patterns of the pulley main body 1 and bearing 2 differ, a slight clearance s is defined between the two (specifically, between the inner surface 1a1 of the pulley main body 1 and the outer surface 2b1 of the outer ring 2b of the bearing 2). This clearance s becomes wider as the radial force L from the belt increases, thus decreasing the joining force between the pulley main body 1 and the outer ring 2b of the bearing 2. For example, for an idler pulley in which the outer diameter of the outer ring 2b of the bearing 2 is 68 mm, the maximum value of said clearance s varies with the belt tension, as shown in FIG. 5.
Therefore, when this type of idler pulley is used with a belt subjected to a heavy radial load, e.g., a timing belt, it receives a rotating force with a weak joining force exerted between the pulley main body 1 and the outer ring 2 of the bearing 2, so that relative rotation (creep) occurs between the pulley main body 1 and the outer ring 2b of the bearing 2, resulting in the wear of the fit surfaces of the pulley main body 1 and the outer ring 2b of the bearing 2. Further, the pulley main body 1 is subjected to a lateral force as when the belt shifts sideways, incurring the possibility of slipping off the bearing outer ring 2b.
Particularly, in the case where the pulley main body is formed of thin steel sheet, it tends to deform and a relatively large clearance develops, thus leading to a problem that phenomena, such as the creep described above, tend to occur.